Poison ivy, like all plants in the cashew family grow lavishly in almost all areas of the U.S. and in southern Canada.  The only places you wont find poison ivy are deserts and areas of extreme heights (> 1500m).  With this diversity of geography comes a diversity of habitats poison ivy can be found in.  The plant can grow in woods, fields, city parks, and gardens.  If it is not an open area (ie a forest) poison ivy is found on the edge because they are not completely shade-tolerant. They persist in wet and dry climates, and also abutting the ocean.  They have a tough outer cuticle for protection and to hold water in.  A strong, substantial root system makes them very hard to get rid of.

The variety of habitats brings a variety of Poison Ivy plant types.   The plant can be in the form of free standing shrubs, extensive ground cover, or vines crawling up trees, fences, or other potential support structures. These contrasting types of growth are caused by the plant responding to internal and external stimuli.  The most vital factor in the lives of plants is light.  Plants are autotrophic and light is the key ingredient that allows the plant to create food for itself.  So what does this have to do with how a plant grows in different habitats? Well this means that Poison Ivy is going to grow towards light, this is an known as phototropism.  Poison ivy is also going to change in growth form once exposed to light.

Once in the presence of light Poison Ivy knows that it can start photosynthesizing so it responds by opening and expanding of the cotyledons and producing chlorophyll.  For this reason, habitats that give Poison Ivy more sunlight will in turn have shorter, greener plants.  This is known as photomorphogenesis.  poison ivy responds and adapts to other environmental factors besides light.  The poison ivy will also change its form in response to touch.  For example, a poison ivy plant growing on a windy beach will have a shorter, stocky stem than the same plant grown in protection of a heavily wooded forest.  This type of responses in known as thigmomorphogenesis.  Another way poison ivy responds to touch is by coiling once it comes in contact with something such as a fence or other tree.  In essence the poison ivy is using the fence, tree, or structure it touches for support as it continues its growth.  This concept of poison ivy’s directional growth for support in response to touch is known as thigmotropism. 

        As you can see poison ivy can live in a number of different habitats in a number of different body types.  However, they all are still one species, Toxicodendron radicans. 

Check out poison ivy’s life cycle

A thigmotrophic Poison Ivy plant!

Poison Ivy bush

The root system

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Poison ivy in the United States